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Password Guidance

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Page 8 <strong>Password</strong> <strong>Guidance</strong> Simplifying Your Approach<br />

Tip 4: Understand the limitations of machinegenerated<br />

passwords<br />

Machine-generated passwords eliminate those passwords that would be simple for an<br />

attacker to guess. They require little effort from the user to create, and, depending on<br />

the generation scheme, can produce passwords that are fairly easy to remember.<br />

The main advantage of machine-generated<br />

schemes is that they eliminate those passwords<br />

that would be simple for an attacker to guess.<br />

They also deliver a known level of ‘randomness’ so<br />

it’s possible to calculate the time it would take to<br />

crack the password using a brute-force attack.<br />

Compared to user-generated schemes, there is no<br />

need to use blacklisting, and user training should<br />

be simpler. They also require little effort from the<br />

user for password creation.<br />

Some machine generation schemes can produce<br />

passwords which are very difficult for people to<br />

remember. This increases both the demand on<br />

helpdesk for resets, and also the likelihood of<br />

insecure storage. They are not recommended.<br />

Instead, use a generation scheme designed for<br />

high memorability (such as passphrases, 4 random<br />

dictionary words or CVC-CVC-CVC 4 style<br />

passwords). Ideally, you should give users a<br />

choice of passwords, so they can select the one<br />

they find the most memorable.<br />

Technical controls<br />

Technical controls such as account lockout,<br />

throttling or protective monitoring are still<br />

relevant when using machine-generated<br />

passwords.<br />

In summary<br />

<br />

<br />

<br />

Choose a scheme that produces<br />

passwords that are easier to remember.<br />

Offer a choice of passwords, so users can<br />

select one they find memorable.<br />

As with user-generated passwords, tell<br />

users that work passwords protect<br />

important assets; they should never reuse<br />

passwords between work and home.<br />

4 Consonant-vowel-consonant constructions

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